Georadar, electromagnetic, and magnetic studies of a landfill and its host sediments

Many landfills are currently causing severe environmental problems, such as ground-water contamination. In view of the large number of poorly documented landfills, fast and inexpensive methods for investigating the shallow subsurface are becoming increasingly important. We have tested a variety of non-intrusive geophysical methods at a landfill located within glacio-fluvial sediments in northwestern Switzerland. Three-dimensional georadar, frequency-domain electromagnetic (EM31), and mag net ie surveys have been conducted over part of the landfill and adjacent undisturbed ground. Dense sampling of the subsurface, a self-designed algorithm for sealing the georadar data in a way that suppressed prominent noise, and application of NMO corrections were important steps for obtaining detailed and accurate images of the investigated area. From borehole information, reflections from interfaces between different gravel sheets and from the top of the underlying lacustrine layer could be identified. Timeslices revealed a general SW-NE flow-direction of the ancient river system that deposited the gravels and sands. The lacustrine sediments are an aquitard in this region. Interpolation of the aquitard, an important barrier for contaminants emanating from the landfill, between surveyareas northwest and southeast of the landfill, provide us with an estimate of the maximum dep th of the waste disposal site.